We intend to continue our studies on the biochemistry of action of cytochalasins. It is hoped to be able to complete the identification of membrane-bound acceptors for these drugs in eukaryotes; to investigate the mechanism of in vitro interaction of selected cytochalasin congeners with presumed receptors of the contractile and cytoskeletal apparatus; and to further probe the newly-found physiological responses of gram (ion) bacteria to cytochalasin A. These investigations will require the preparation of high specific activity radiolabeled drugs as well as a number of drug analogs with potential affinity-labeling and spin-labeling functions. Co-metabolism technics will also be used to search for novel cytochalasin derivatives and cytotoxic analogs. The accellular slime mold P. polycephalum shows high promise as a model system for exploration of many of these set forth goals. In collaborative efforts with investigators using cultured mammalian cells, structure-function activity of the cytochalasins will be further delineated.